1. Field of the Invention
This invention relates generally to the field of flavonoids, and more specifically to forms of flavonoids that possess increased bioavailability for nutritional, pharmaceutical and cosmetic applications.
2. Description of Related Art
References to the publications and other reference materials to describe the backgound of the invention and to provide additional detail regarding its practice are hereby incorporated by reference. For convenience, the reference materials are numerically referenced and grouped in the appended bibliography.
Silymarin, a polyphenolic flavonoid mixture isolated from milk thistle, Silybum marianum (L.) Gaertn, is composed mainly of three isomers: silidianin, ilichristin and the major component, silibinin. Silymarin components are in a unique class of natural products, known as flavonolignans, produced in the plant by radical coupling of dihydroquercetin and coniferyl alcohol. Silibinin (see FIG. 1, where R1=R2=R3=H) has been found to exist as a mixture of two diastereomers (1) (2R, 3R, 12S, 13S and 2R, 3R, 12R, 13R). In general, it has been shown that the biological activities of Silymarin are associated with the major component, silibinin (2, 3). Silibinin also is known as silybin.
Silymarin is commonly used as a nutritional supplement. It has been shown to protect the liver against the negative effects of toxins present in food, air and water. In general, silymarin is used to restore normal liver function (4).
Silibinin has been found to possess a wide variety of biological activities, including hepato-protection (5) and inhibition of breast (6), prostate (7) and skin (8) tumor development.
Previous investigations of the application of silibinin and/or silymarin on the skin have demonstrated inhibition of photocarcinogenesis (9), inhibition of inflammation (10), reversal of skin aging (11, 12, 13) and treatment of dermatological conditions, like psoriasis and dermatitis (14). Silymarin also has been found to stimulate hair regrowth (15).
Previous studies have relied on the use of silymarin as extracts that typically are standardized on the amount of silibinin present. In general, the use of extracts creates a number of problems. For example, the composition of the extract usually is not completely determined, resulting in uncertainty in the relationship of chemical components and their biological activities. Furthermore, unidentified components present in extracts might cause negative side effects.
In general, it is well known that silymarin and silibinin are not readily soluble in aqueous or lipophilic phases (Merck Index, Reference 8680). Furthermore, once they reach the bloodstream, then they are readily metabolically transformed to glucuronide and sulfate conjugates, and cleared in the urine. Both of these properties result in poor bioavailability of silibinin or silymarin, thereby limiting their effectiveness.
One strategy for enhancing the absorption of silibinin is to convert silibinin into lipophilic complexes with phospholipids (16). Another approach involves the chemical modification of silibinin to form the 3,11-dihemisuccinate salt of silibinin (17).
The present invention provides hydrophilic and lipophilic pro-forms of silibinin. The hydrophilic pro-forms have the formula 
In this formula, one or more of R1, R2, and R3 are independently selected from the group consisting of cationic esters, anionic esters, neutral esters, and H.
Pharmaceutical compositions of the hydrophilic pro-forms of silibinin are suitable for topical or oral administration in an individual. The pharmaceutical composition includes a hydrophilic silibinin pro-form and a pharmaceutically acceptable carrier.
In another aspect, the invention is directed to lipophilic pro-forms of silibinin. The lipophilic pro-forms have the formula 
wherein
one or more of R1, R2, and R3 are independently selected from the group consisting of aliphatic acid residues, aromatic acid residues, and H.
Pharmaceutical compositions of the lipophilic pro-forms of silibinin are suitable for topical or oral administration in an individual. The pharmaceutical composition includes a lipophilic pro-form of silibinin and a pharmaceutically acceptable carrier.
Other features of the invention are directed to methods of treating a subject having or at risk of having a cell proliferative disorder by administering to the subject a therapeutically effective amount of a silibinin pro-form, hydrophilic form or lipophilic form depending on the indication, which include breast cancer, skin cancer, uterine cancer, testicular cancer, lung cancer, prostate cancer, and liver cancer. Another method of the invention is directed to decreasing oxidative stress in a subject having a disorder associated with oxidative stress by administering to the subject a therapeutically effective amount of a silibinin pro-form.
The above-discussed and many other features and attendant advantages of the present invention will become better understood by reference to the following detailed description of the invention taken in conjunction with the accompanying drawing.